Nh3 containing plasma nitridation of a layer on a substrate

ABSTRACT

Methods and apparatus for forming nitrogen-containing layers are provided herein. In some embodiments, a method includes exposing a first layer of a substrate to a plasma formed from a process gas comprising predominantly a mixture of ammonia (NH 3 ) and a noble gas, wherein ammonia is about 0.5 to about 15 percent of the process gas; and maintaining the process chamber at a pressure of about 10 mTorr to about 80 mTorr while exposing the first layer to the plasma to transform at least an upper portion of the first layer into a nitrogen-containing layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/504,685, filed Jul. 5, 2011, which is herein incorporated byreference.

FIELD

Embodiments of the present invention generally relate to semiconductorprocessing, and more particularly to methods for formingnitrogen-containing layers.

BACKGROUND

The scaling of semiconductor devices, such as dynamic random accessmemory (DRAM), logic devices, and the like, may be limited by gateleakage (J_(g)). For example, as thickness of a gate dielectric layer isscaled, current may leak between the channel and the gate of atransistor device causing device failure. The gate leakage may bereduced by incorporating nitrogen into the gate dielectric layer. Forexample, a gate dielectric layer at the 32 nm node may comprise siliconoxynitride (SiON), where the presence of nitrogen reduces gate leakagein the device.

Typically, nitrogen is incorporated into the gate dielectric layer by aplasma nitridation process that provides for gate leakage reduction atthe expense of other desired properties, for example, flat band voltage(V_(fb)), threshold voltage (V_(t)), and mobility. For example,increased nitrogen content in the gate dielectric layer may undesirablyincrease V_(t) and excessively decrease mobility. Further, oxygen maydiffuse from the gate dielectric layer under typical processingconditions, thus further reducing device performance, for example bydegrading the dielectric properties of the gate dielectric layer.

Accordingly, there is need in the art for a method of forming gatedielectric layers having reduced gate leakage at smaller device nodeswithout reducing device performance.

SUMMARY

Methods and apparatus for forming nitrogen-containing layers areprovided herein. In some embodiments, a method includes exposing a firstlayer of a substrate to a plasma formed from a process gas comprisingpredominantly a mixture of ammonia (NH₃) and a noble gas, whereinammonia is about 0.5 to about 15 percent of the process gas; andmaintaining the process chamber at a pressure of about 10 mTorr to about80 mTorr while exposing the first layer to the plasma to transform atleast an upper portion of the first layer into a nitrogen-containinglayer The preceding brief summary is not intended to be limiting of thescope of the present invention. Other and further embodiments of thepresent invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a flow chart depicting a method of forming anitrogen-containing layer in accordance with some embodiments of theinvention.

FIGS. 2A-D depict stages of fabricating a gate dielectric layer inaccordance with some embodiments of the invention.

FIG. 3 depicts a plasma nitridation reactor suitable for use inaccordance with some embodiments of the invention.

FIG. 4 depicts a substrate support suitable for use in a plasmanitridation reactor in accordance with some embodiments of theinvention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Methods and apparatus for forming nitrogen-containing layers areprovided herein. The inventive methods and apparatus may advantageouslyprovide improved nitridation of a target layer (e.g., a first layer) forexample, by facilitating increased nitrogen content, and improved oxygenretention at an interface between the target layer and another devicelayer, for example, a polysilicon gate.

FIG. 1 depicts a nitridation process 100 for forming anitrogen-containing layer in accordance with some embodiments of thepresent invention. Generally, the process 100 includes providing apartially fabricated semiconductor structure including a substratehaving a first layer disposed thereon. The semiconductor structure maybe a partially fabricated semiconductor device such as Logic, DRAM, orFlash memory devices. The nitrogen-containing layer formed by thisprocess may be one or more of a gate dielectric layer, a tunnel oxidelayer, a spacer layer, or any suitable layer of a semiconductorstructure that may benefit from nitridation, for example, to reducejunction leakage, gate leakage, or the like.

The process 100 is described herein with respect to the partiallyfabricated semiconductor structure depicted in FIGS. 2A-D, whichrespectively depict stages of fabrication of a semiconductor structureincluding a first layer formed over a substrate. The nitridation process100 may be performed in any suitable plasma reactor, for example, suchas those reactors configured to provide an inductively coupled,capacitively coupled plasma, or remote plasmas, or other plasma types.Embodiments of suitable plasma reactors that may be utilized with theinventive methods are described below with respect to FIG. 3. The plasmareactor may be utilized alone or, more typically, as a processing moduleof an integrated semiconductor substrate processing system, or clustertool, such as a CENTURA® DPN Gate Stack integrated semiconductor waferprocessing system, available from Applied Materials, Inc. of SantaClara, Calif. Other tools, including those available from othermanufacturers, may also be used.

The process 100 begins at 102, where a substrate 202 is provided havinga first layer 204 to be nitridized disposed thereon, as shown in FIG.2A. The substrate 202 and the first layer 204 may be part of acompletely or partially fabricated semiconductor device 200. Thesubstrate 202 may have various dimensions, such as 200 or 300 mmdiameter wafers, as well as rectangular or square panels. The substrate202 may comprise a material such as crystalline silicon (e.g., Si<100>or Si<111>), silicon oxide, strained silicon, silicon germanium, dopedor undoped polysilicon, doped or undoped silicon wafers, patterned ornon-patterned wafers, silicon on insulator (SOI), carbon doped siliconoxides, silicon nitride, doped silicon, germanium, gallium arsenide,glass, sapphire, or the like.

The semiconductor device 200 may be completely or partially formed uponthe substrate 202 and includes at least the first layer 204 to benitridized. The semiconductor device 200 (when completed) may be, forexample, a field effect transistor (FET), dynamic random access memory(DRAM), a flash memory device, a 3D FINFET device, or the like. Thefirst layer 204 may be, for example, utilized as a gate dielectric layerof a transistor device, a tunnel oxide layer in a flash memory device, aspacer layer atop a gate structure, an inter-poly dielectric (IPD) layerof a flash memory device, or the like. The first layer 204 may have anythickness suitable in accordance with the particular application forwhich the first layer 204 may be utilized. For example, the first layer204 may have a thickness of about 0.5 to about 10 nm. The first layer204 may comprise an oxide layer, such as silicon oxide (SiO₂), hafniumoxide (HfO₂), hafnium silicate (HfSiO_(x)), or any suitable oxide layerused in a semiconductor device and requiring nitridation. For example,in some embodiments, the oxide layer may be a native oxide layer, orformed by any suitable oxidation process including the oxidation processdiscussed below. The first layer 204 need not be limited to an oxidelayer, and other suitable layers may benefit from the inventive methodsdisclosed herein. For example, other suitable embodiments of the firstlayer 204 may include other silicon-containing layers such as SiC, orthe like. The layer 204 can also be a stack of layers, such as a firstsub-layer of SiO₂ and a second sub-layer of HfO₂ or a first sub-layer ofSiO₂ and a second sub-layer of HfSiO_(x), or the like.

Next, at 104, the substrate 202 may be heated prior to and duringnitridation. Heating the substrate 202 may facilitate providingincreased nitrogen content into the first layer 204 and improved deviceproperties. For example, heating the substrate 202 to a temperature ofat least about 250 degrees Celsius, or at least about 350 degreesCelsius may facilitate increased nitrogen content (e.g., an atomicpercentage content of about 5 to about 35) in the first layer 204. Insome embodiments, the substrate may be heated to a temperature of about250 to about 550 degrees Celsius, or in some embodiments, about 350 toabout 450 degrees Celsius. The actual maximum substrate temperature mayvary based upon hardware limitations and/or the thermal budget of thesubstrate being processed.

In embodiments where the first layer 204 is an oxide layer, theincreased temperature may advantageously facilitate less evolution ofoxygen from the layer (e.g., less than about 20%) and further,accumulation of oxygen at an interface of the first layer 204 and thesubstrate 202. In some embodiments, the substrate 202 is heated to about250 to about 550 degrees Celsius. In some embodiments where the firstlayer 204 is an oxide layer, the substrate 202 may be heated to about300 to about 550 degrees Celsius, or to about 350 to about 500 degreesCelsius.

In some embodiments, the substrate 202 may be positioned in the reactorsuch that heat transfer to the substrate is maximized, for example,between the substrate 202 and a substrate support on which the substrate202 rests during the nitridation process 100. As such, the substrate 202may be secured to the substrate support using a chucking device, such asan electrostatic chuck (ESC), a vacuum chuck, or other suitable device.Chucking the substrate 202 may advantageously facilitate reproducibleheat transfer even at low pressures (the process pressure region), forexample, at about 4 mTorr to about 1 Torr, or at about 10 to about 80mTorr, at about 10 to about 40 mTorr, or at about 10 to about 20 mTorr.Optionally, in embodiments where an electrostatic chuck is provided tosecure the substrate 202, a second plasma may be formed above thesubstrate 202 to facilitate stabilization of the substrate temperatureas the substrate is chucked. For example, the second plasma may beformed from a non-reactive gas including at least one of argon (Ar),helium (He), krypton (Kr), xenon (Xe), or the like, to preheat thesubstrate 202 such that upon chucking the substrate 202 to the substratesupport and extinguishing the plasma, the substrate 202 does notexperience a dramatic change in temperature which could lead to processvariation and/or wafer breakage. As used herein, non-reactive gasesinclude gases that do not substantially react with the substrate (e.g.,do not substantially deposit upon or etch the substrate).

The substrate 202 may be heated by any suitable heating mechanismcapable of increasing and maintaining the substrate temperature at about250 degrees Celsius or greater or, in some embodiments, at about 350degrees Celsius or greater. Suitable heating mechanisms can includeresistive heating, radiative heating or the like. For example, and asdiscussed below in embodiments of the reactor 300, one or more resistiveheaters may be disposed in a substrate support for providing heat to thesubstrate 202. Alternatively, the substrate may be heated, for example,by one or more lamps or other energy sources disposed above and/or belowthe substrate 202.

In one heating approach, the heater elements are embedded in theelectrostatic chuck, so that the substrate is directly heated from theelectrostatic chuck. Several advantages may arise from such approach:(1) the substrate can be maintained at a constant temperature during theentire process as long as it is chucked, even though the processpressure is as low as 4 mTorr; (2) process results (nitrogen dose andpercentage of nitrogen incorporated by mass (N %)) can be reproduciblefrom substrate to substrate due to the tight control on the substratetemperature during the process; and (3) the within-substrate nitridationuniformity pattern can be altered (e.g., compensated for) by carefullydesigned heating uniformity pattern in the heater elements of theelectrostatic chuck, or by providing multi-zone heater elements havingindependent control.

In the case of using an electrostatic chuck heater, due to the nature ofchucking/heating process, the rise of the substrate temperature can bevery fast, such as up to about 30 degrees Celsius per second. Under suchhigh heating rates, there may be a chance that not every portion of thewafer will be heated at the same rate, so that at certain point, thetemperature difference within the substrate may reach a critical value(e.g., >75 degrees Celsius) which could cause the substrate (such as asemiconductor wafer) to crack. To prevent such failure, a preheat stepmay be implemented prior to substrate chucking. The preheat step mayinclude flowing a non-reactive gas, such as nitrogen (N2) or helium(He), or the like, at a rate of about 400 sccm to about 4 liter perminute, for about 20 to about 60 seconds or more (such as about 50seconds), at a pressure of about 1-10 Torr (such as about 8 Torr), whilemaintaining the electrostatic chuck heater at the desired temperature(such as about 400 degrees Celsius) with the substrate disposed on thesurface of the electrostatic chuck but not chucked thereto. The preheatstep facilitates bringing up the substrate temperature close to theelectrostatic chuck temperature prior to chucking (for example to withinabout 150 degrees Celsius of a targeted temperature of the substrate),hence reducing the potential thermal shock to the substrate uponchucking the substrate. In some embodiments, when a low contactelectrostatic chuck (e.g., an electrostatic chuck having up to about 5%contact area) is utilized to support the substrate, a backside gas maybe utilized to preheat the wafer. In some embodiments, the substrate maybe preheated prior to delivery into the process chamber, such as bycontact or non-contact (e.g., lamp) methods.

In some embodiments, to control or maintain the temperature of thesubstrate 202 at a desired temperature, or within a desired temperaturerange, the backside of the substrate 202 may be exposed to a heattransfer gas. In typical nitridation processes, the heat transfer gasmay be helium (He), or another inert gas, such as nitrogen (N₂).Unfortunately, due to surface roughness on the backside of the substrate202, some heat transfer gas may leak into a processing volume of anitridation reactor and affect the nitridation rate, composition of anitridizing plasma, process uniformity, reactor pressure, or the like.The risk and/or amount of such leakage may be further increased by lowpressures in the reactor. To limit at least some of the undesirableeffects that may be caused by heat transfer gas leakage, a process gas(e.g., a gas utilized for processing the substrate during the inventivemethods disclosed herein) may be used as the heat transfer gas. Theprocess gas may be, for example, a nitrogen-containing gas such asnitrogen (N₂), ammonia (NH₃), or combinations thereof. Thus, leakage ofthe process gas being used as a heat transfer gas from the backside ofthe substrate 202 may have a limited or no effect on the nitridationprocess.

Optionally, prior to nitridation of the first layer 204, the processchamber may be pre-conditioned to reduce residual oxygen content in theprocessing volume. For example, residual oxygen content such as frommoisture, water (H₂O) or the like may result in undesired parasiticoxidation of the substrate 202 or the first layer 204. To prevent thisfrom happening, the interior of the process chamber (including the lid,sidewall, and pedestal or chuck) may be pre-conditioned with apre-conditioning plasma formed from a pre-conditioning gas. Thepre-conditioning gas may include, for example, an inert gas, hydrogen(H₂) and an inert gas, ammonia (NH₃), hydrogen (H2) and nitrogen (N₂),or any suitable gas and/or combination of gases that may be reactivewith oxygen and/or oxygen-containing gases. In some embodiments,pre-conditioning may be performed prior to, or during, chucking (e.g.,securing the substrate to the chuck). In some embodiments,pre-conditioning may be performed prior to heating the substrate, orprior to nitridation of the first layer 204.

Next, at 106, the first layer 204 may be exposed to a radio frequency(RF) plasma formed from a process gas of a mixture of 0.5 percentammonia (NH₃) with the balance being a noble gas, while maintaining theprocess chamber at a pressure of about 4 mTorr to about 1 Torr, or about10 to about 80 mTorr, or about 10 mTorr to about 40 mTorr, or about 10mTorr to about 20 mTorr to form a nitrogen-containing layer 208, asdepicted in FIGS. 2C and 2D. For example, in some embodiments, theprocess gas may be ammonia (NH₃) or a mixture of ammonia (NH₃) and anoble gas wherein the mixture contains at least 0.5 percent of ammonia(NH₃). The noble gas may be, for example, argon (Ar), helium (He),krypton (Kr), or the like. In some embodiments, the process gascomprises ammonia (NH₃) and argon (Ar). In some embodiments, the processgas may consist only of ammonia and the noble gas. In some embodiments,the process gas may be predominantly comprised of or may consistessentially of ammonia and the noble gas.

In some embodiments, the process gas may be supplied at a total gas flowfrom about 100 to about 1000 sccm, or at about 400 sccm (although otherflow rates may be used depending upon the application and configurationof the process chamber). In some embodiments, the process gas maycomprise about 10-100 percent NH₃ (e.g., an NH₃ flow of between about10-1000 sccm). In some embodiments, the process gas may comprise about0.5-99 percent NH₃ (e.g., an NH₃ flow of between about 0.5-990 sccm)with the balance being essentially a noble gas, for example, argon (Ar)(e.g., a noble gas percentage of about 1 to about 99.5 percent). In someembodiments, the process gas may be about 0.5-15 percent NH₃ (e.g., anNH₃ flow of between about 5-150 sccm) with the balance being essentiallya noble gas, such as argon (e.g., an inert gas percentage of about 85 toabout 99.5 percent). In some embodiments, the process gas may be about0.5-10 percent NH₃ (e.g., an NH₃ flow of between about 5-100 sccm) withthe balance being essentially a noble gas, such as argon (e.g., an inertgas percentage of about 90 to about 99.5 percent). In some embodiments,the process gas may be about 1-5 percent NH₃ (e.g., an NH₃ flow ofbetween about 5-100 sccm) with the balance being essentially a noblegas, such as argon (e.g., an inert gas percentage of about 95 to about99 percent). In some embodiments, the process gas may be about 2.5percent of NH₃ (e.g., an NH₃ flow of about 25 sccm when 1000 sccm totalgas flow is provided) with the balance being essentially an inert gas,such as a noble gas, for example, argon (e.g., an inert gas percentageof about 97.5 percent). [WEI: PLEASE CONFIRM/CORRECT RANGES ANDCOMPOSITION. WE WOULD LIKE TO CLAIM WIDER RANGE, NARROWER RANGE, ANDNARROWEST RANGE. WE BASED THE 0.5-10 and 1-5 PRECENT RANGES ON THEPREFERRED AMOUNT OF NH3 BEING 2.5 PERCENT. ANY OTHER GASES PERMISSIBLEOR DESIRABLE?]

The use of NH₃ in the process gas advantageously provides NH radicalsfor gate oxide nitridation. The inventors have observed that nitridationof SiON film using a NH₃—Ar process gas advantageously provides lowerleakage current compared to traditional N₂ plasma nitridation processes.

Moreover, the inventors have observed that variations in the NH₃percentage in a NH₃—Ar process gas mixture results in changes in Hradical concentrations in the resulting plasma. For example, in someembodiments, the inventors have discovered that a decrease of NH₃ in theprocess gas from 20% to 2.5% results in an approximately 50% decrease inthe concentration of H radicals in the plasma. The decrease inconcentration of H radicals, which can react with chamber parts such asaluminum anodization layers, advantageously minimizes damage to theprocess tool. However, it was unexpectedly discovered that such adramatic decrease in the amount of NH₃ provided, while significantlylowering the concentration of H radicals in the plasma, did notsignificantly alter nitridation levels of the process. As such, theinventors have unexpectedly discovered that the amount of ammonia usedduring the process can be lowered to advantageously minimize damage tothe process tool while substantially retaining process performance andthroughput.

The process gas may be introduced into a plasma reactor, for example,the plasma reactor 300, and used to form a plasma. In some embodiments,the plasma density may be about 10¹⁰ to about 10¹² ions/cm³. The plasmamay be formed by using an RF source power. In some embodiments, the RFsource power is up to about 5000 Watts. The RF source power may beprovided at any suitable RF frequency. For example, in some embodiments,the RF source power may be provided at a frequency about 2 to about 60MHz.

The plasma 206 may be pulsed or continuously applied at up to about 5000Watts. For example, the plasma 206 may applied continuously at up toabout 5000 Watts for a duration of about 10 to about 240 seconds, orabout 60 seconds. The duration may be adjusted (e.g., shortened) tolimit damage to the device 200. Alternatively, the plasma 206 may bepulsed at a pulse frequency of about 4 kHz to about 15 kHz. The pulsedplasma may have a duty cycle of about 2% to about 70%, at up to 2000watts peak power, where the duty cycle and/or RF source power may beadjusted to limit damage to the device 200. In some embodiments, thepulsed plasma may have a duty cycle of about 30% to about 70%, at up to4000 Watts peak power, where the duty cycle and/or RF source power maybe adjusted to limit damage to the device 200.

In some embodiments, the exposed surface of the substrate 202 may be atleast partially covered with a sacrificial layer (not shown), such as amasking layer to prevent exposure to the plasma 206 (e.g., to limitexposure of the plasma to desired portions of the substrate 202 and/orthe first layer 204). In some embodiments, a pressure in the plasmareactor may be up to about 80 mTorr, about 10 mTorr to about 80 mTorr,about 10 mTorr to about 40 mTorr, or about 10 to about 30 mTorr duringthe exposure of the first layer 204 to the plasma 206.

In some embodiments, the nitridation rate may be improved by applying anRF bias to the substrate 202. For example, about 20 to about 60 Watts ofRF bias power may be applied at a frequency of about 2 MHz to about 60MHz. Such low RF bias may facilitate improving nitridation rates withoutcausing excessive ion bombardment on the device 200.

The nitrogen-containing layer 208 formed from exposure of the firstlayer 204 to the plasma 206 as discussed above may be, for example,utilized as a gate dielectric layer of a transistor device, a tunneloxide layer in a flash memory device, a spacer layer atop a gatestructure, in an inter-poly dielectric (IPD) layer of a flash memorydevice, or the like. The nitrogen-containing layer 208 may have athickness of about 0.3 to about 10 nm. The nitrogen-containing layer 208may have a nitrogen content of about 5 to about 35 atomic percent. Thenitrogen-containing layer 208 may comprise an oxynitride layer, such assilicon oxide (SiON), hafnium oxynitride (HfON), nitridated hafniumsilicate (HfSiON), or any suitable oxynitride layer used in asemiconductor device and requiring nitridation. The nitrogen-containinglayer 208 need not be limited to an oxynitride layer, and other suitablelayers may benefit from the inventive methods disclosed herein. Forexample, in other suitable embodiments, the nitrogen-containing layer208 may include or may be replaced with SiCN or other silicon (Si)containing compounds, metal containing compounds such as titanium oxideor nitride, tantalum oxide or nitride, aluminum oxide or nitride, or thelike.

Upon forming the nitrogen-containing layer 208, the process 200generally ends and additional process steps (not shown) may be performedto complete fabrication of the semiconductor device 200 and/or otherdevices (not shown) on the substrate 202. For example, and as shown inFIG. 2D, a conducting layer 214, such as polysilicon or another suitableconducting material, such as a metal, may be deposited atop thenitrogen-containing layer 208 and configured as a control gate of thedevice 200. Additional process steps may include ion implantation toform source/drain regions 210 in the substrate 202 adjacent to thenitrogen-containing layer 208 and conducting layer 214. The source/drainregions 210 have a channel 212 disposed therebetween, where thenitrogen-containing layer 208 is disposed atop the channel 212. Usingthe inventive nitridation processes described herein gate leakagebetween the channel and the control gate is about 0.01 to about 1Amp/cm² for a nitrogen-containing layer 208 having about 15 to about 30atomic percent nitrogen content and a thickness of about 10 to about 20angstroms.

The inventive methods described herein, for example, the nitridationprocess 100 can be performed in a plasma reactor. For example, FIG. 3depicts a schematic diagram of an inventive plasma reactor 300 adaptedto be used to practice embodiments of the invention as discussed herein.The reactor 300 may be utilized alone or, more typically, as aprocessing module of an integrated semiconductor substrate processingsystem, or cluster tool, such as a CENTURA® DPN Gate Stack integratedsemiconductor wafer processing system, available from Applied Materials,Inc. of Santa Clara, Calif.

The reactor 300 includes a process chamber 310 having a substratesupport 316 disposed within a conductive body (wall) 330, and acontroller 340. In some embodiments, the substrate support (cathode) 316is coupled, through a first matching network 324, to a biasing powersource 322. The biasing source 322 generally is a source of up to 500 Wat a frequency of approximately 13.56 MHz that is capable of producingeither continuous or pulsed power. In other embodiments, the source 322may be a DC or pulsed DC source. In some embodiments, no bias power isprovided.

In some embodiments, the process chamber 310 may include a liner (notshown) to line the inner surfaces of the process chamber 310. In someembodiments, the liner may be cooled, for example with coolant channelsprovided within the liner to flow a coolant therethrough. In someembodiments, the process chamber 310 (and other components exposed toplasma during processing) may be coated with a material that isresistant to the plasma. For example, in some embodiments, the processchamber 310 may be coated with a material that is resistant to attackfrom the plasma. In some embodiments, the coating may comprise a quartz,or a ceramic material, such as a yttrium oxide (Y₂O₃)-based ceramiccompositions, aluminum oxide, or the like. In accordance withembodiments of the present invention, attack of chamber components fromhydrogen radicals may advantageously be reduced during processing asdescribed herein, while advantageously maintaining nitridation rates.

The chamber 310 may be supplied with a substantially flat dielectricceiling 320. Other modifications of the chamber 310 may have other typesof ceilings such as, for example, a dome-shaped ceiling or other shapes.At least one inductive coil antenna 312 is disposed above the ceiling320 (dual co-axial antennas 312, including an outer coil 312 _(A) and aninner coil 312 _(B), are shown in FIG. 3). Each antenna 312 is coupled,through a second matching network 319, to a RF power source 318. The RFsource 318 typically is capable of producing up to about 5000 W at atunable frequency in a range from 2 MHz to 13.56 MHz, and which mayproduce either a continuous or pulsed plasma. Typically, the wall 330may be coupled to an electrical ground 334.

In some embodiments, a power divider 304 may be disposed in the linecoupling the outer coil 312 _(A) and the inner coil 312 _(B) to the RFpower source 318. The power divider 304 may be utilized to control theamount of RF power provided to each antenna coil (thereby facilitatingcontrol of plasma characteristics in zones corresponding to the innerand outer coils). The dual coil antenna configuration may advantageouslyprovide improved control of nitrogen dosage within each zone, such as tothe first layer 204, as discussed above in the method 100.

Optionally, either and/or both of the antennas 312 may be tilted and/orraised lowered with respect to the ceiling 320. The change in positionand/or angle of the antenna 312 may be utilized, for example, to changethe characteristics, such as uniformity, of a plasma formed in theprocess chamber.

Further, and optionally, a plasma shield/filter may be included abovethe substrate support to provide improved control of, for example,nitridation of the first layer 204 as discussed above in the method 100.The plasma shield/filter may comprise a material, such as quartz, andmay be grounded to the chamber 310 to remove ion species from the plasmaformed in the process chamber. For example, an ion-radical shield 327may be disposed in the chamber 310 above the substrate support 316. Theion-radical shield 327 is electrically isolated from the chamber walls330 and the substrate support 316 and generally comprises asubstantially flat plate 331 having a plurality of apertures 329. In theembodiment depicted in FIG. 3, the ion-radical shield 327 is supportedin the chamber 310 above the pedestal by a plurality of legs 325. Theapertures 329 define a desired open area in the surface of theion-radical shield 327 that controls the quantity of ions that pass froma plasma formed in an upper process volume 378 of the process chamber310 to a lower process volume 380 located between the ion-radical shield327 and the substrate 314. The greater the open area, the more ions canpass through the ion-radical shield 327. As such, the size anddistribution of the apertures 329, along with the thickness of the plate331 controls the ion density in volume 380. Consequently, the shield 327is an ion filter. One example of a suitable shield that may be adaptedto benefit from the invention is described in U.S. patent applicationSer. No. 10/882,084, filed Jun. 30, 2004 by Kumar, et al., and entitled“METHOD AND APPARATUS FOR PHOTOMASK PLASMA ETCHING,” which is herebyincorporated by reference in its entirety. By changing the ion densitynear the wafer surface, one can control the ion/radical ratio, hence,possibly controlling the nitridation profile.

In some embodiments, the substrate support 316 may include a chuckingdevice 317 for securing the substrate 314 to the support pedestal duringprocessing. For example, the chucking device 317 may include anelectrostatic chuck or a vacuum chuck. The chucking device 317 mayfacilitate improved heat transfer between the substrate 314 and one ormore resistive heaters 321 disposed in the substrate support 316. Asillustrated, the one or more resistive heaters 321 may be disposed inthe substrate support 316 generally below the position of substrate 314and configured in multiple zones to facilitate controlled heating of thesubstrate 314. In some embodiments, the substrate support 316 includesan electrostatic chuck and also includes one or more resistive heatersdisposed within or beneath the electrostatic chuck. In some embodiments,the substrate support 316 may not include an electrostatic chuck, butmay have one or more resistive heaters disposed proximate a supportsurface of the substrate support. In such embodiments, the substratesupport having the resistive heaters may have a surface coating of, forexample, aluminum nitride (e.g., the substrate support may be fabricatedfrom, or may have an outer coating of, aluminum nitride or the like).

In some embodiments, the substrate support 316 may not have anelectrostatic chuck and may include a resistive heater, such as shown inFIG. 4. The substrate support 316 depicted in FIG. 4 includes aresistive heater 321 configured to regulate the temperature of thesubstrate 314. The heater 321 may be include one or more zones (outerzone 402 and inner zone 404 depicted in FIG. 4). The heater 321 iscoupled to a power source 412 and is capable of maintaining thesubstrate 314 at a temperature of up to about 500 degrees Celsius. Insome embodiments a grounding mesh 406 may be disposed between the one ormore heaters 321 and an upper surface 416 of the substrate support 316to prevent the substrate 314 form sticking to the surface 416 of thesubstrate support 316. The inert coating discussed above may be alsoapplied to the surface 416 of the substrate support 316.

In the case of using an electrostatic chuck with a heater, it has beendemonstrated that the nitrogen dose and N % (e.g., the percentage ofnitrogen by mass incorporated into the first layer 204 to form thenitrogen-containing layer 208) is directly proportional to the wafertemperature during the plasma process. So to control and/or tune thenitrogen dose and N % uniformity on the wafer, two approaches can beutilized: (1) fixed zone heating with a pre-designed pattern of powerdensity for the heater elements so that the temperature uniformitypattern of the wafer compensates for the plasma uniformity pattern; or(2) tunable multiple zone heating with tunable power supplies fordifferent heater zones (typically center and edge dual zones, but morezones may be utilized) so that the wafer temperature uniformity can betuned to compensate for the plasma uniformity pattern. In eitherapproach, temperature may be utilized as a knob to achieve improvedwithin-wafer nitridation uniformity and/or providing a desired nitrogendose pattern in the substrate. In some embodiments, the nitrogen dosepattern may be substantially uniform (e.g., within about 1 percent).

A motion assembly 410 may be provided to control the elevation of thesubstrate support 316, and therefore, of the substrate 314 duringprocessing. The motion assembly 410 is sealingly coupled to the chamberbody 330 using a flexible bellows 408. Alternatively or in combination,the motion assembly 410 may be configured to rotate the substratesupport 316.

Returning to FIG. 3, alternatively or in combination, one or moreradiative sources, such as lamps 323, may be provided to heat thesubstrate 314. The lamps 323 may be configured similar to radiativelamps utilized in rapid thermal processing chambers. Other heatingmethods or designs, including heating the substrate from above, may alsobe used.

The temperature of the substrate 314 may be controlled by stabilizing atemperature of the substrate support 316. A heat transfer gas from a gassource 348 is provided via a gas conduit 349 to channels formed by theback of the wafer 314 and grooves (not shown) in the support surfaceand/or chucking device 317. The heat transfer gas is used to facilitateheat transfer between the substrate support 316 and the substrate 314.During the processing, the substrate support 316 may be heated by theone or more resistive heaters 321 to a steady state temperature and thenthe heat transfer gas facilitates uniform heating of the substrate 314.Using such thermal control, the substrate 314 may be maintained at atemperature of about 0 to about 550 degrees Celsius.

In some embodiments, the substrate support 316 may have a low thermalmass for example, to prevent thermal shock to the substrate die to rapidcooling. For example, the substrate support 316 may be configuredwithout a heat sink or cooling plate coupled thereto, thereby limitingthe rate at which heat may be removed from the substrate support 316.

During a typical operation, the substrate 314 (e.g., the substrate 202)may be placed on the substrate support 316 and process gases aresupplied from a gas panel 338 through an entry port 326 disposed in theceiling 320 and centered above the substrate 314. In some embodiments,the gas panel 338 is configured to supply process gases such as ammonia(NH₃) or hydrogen (H₂). The process gases may be combined withadditional gases, for example, nitrogen (N₂), helium (He) or argon (Ar)and flowed into the chamber 310 via the entry port 326. The entry port326 may include, for example, a baffle or similar gas inlet apparatusthat can provide a process gas perpendicularly towards the substrate 314and radially onward into the process chamber 310. Upon entering theprocess chamber 310 via the entry port 326, the process gases form agaseous mixture 350. The gaseous mixture 350 is ignited into a plasma355 in the chamber 310 by applying power from the RF source 318 to theantenna 312. Optionally, power from the bias source 322 may be alsoprovided to the substrate support 316. The pressure within the interiorof the chamber 310 is controlled using a throttle valve 362 and a vacuumpump 336. The temperature of the chamber wall 330 is controlled usingliquid-containing conduits (not shown) that run through the wall 330.

The controller 340 comprises a central processing unit (CPU) 344, amemory 342, and support circuits 346 for the CPU 344 and facilitatescontrol of the components of the nitridation process chamber 310 and, assuch, of nitridation processes, such as discussed herein. The controller340 may be one of any form of general-purpose computer processor thatcan be used in an industrial setting for controlling various chambersand sub-processors. The memory, or computer-readable medium, 342 of theCPU 344 may be one or more of readily available memory such as randomaccess memory (RAM), read only memory (ROM), floppy disk, hard disk, orany other form of digital storage, local or remote. The support circuits346 are coupled to the CPU 344 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like. Theinventive method may be stored in the memory 342 as software routine andmay be executed or invoked in the manner described above. The softwareroutine may also be stored and/or executed by a second CPU (not shown)that is remotely located from the hardware being controlled by the CPU344.

Thus, methods and apparatus for forming nitrogen-containing layers havebeen provided herein. The inventive methods and apparatus mayadvantageously provide improved nitridation of a target layer (e.g., afirst layer) by facilitating increased nitrogen content with reducedlayer thickening, and improved oxygen retention at an interface betweenthe target layer and another device layer, for example, a polysilicongate.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A method of forming a nitrogen-containing layer, comprising: exposinga first layer of a substrate to a plasma formed from a process gascomprising predominantly a mixture of ammonia (NH₃) and a noble gas,wherein ammonia is about 0.5 to about 15 percent of the process gas andthe noble gas is predominantly the balance; and maintaining the processchamber at a pressure of about 10 mTorr to about 80 mTorr while exposingthe first layer to the plasma to transform at least an upper portion ofthe first layer into a nitrogen-containing layer.
 2. The method of claim1, further comprising: exposing the first layer to a second plasmaformed from a non-reactive gas prior to exposing the first layer to theplasma formed from the process gas; securing the substrate to thesubstrate support using an electrostatic chuck or a vacuum chuck whileexposing the first layer to the second plasma.
 3. The method of claim 2,further comprising: preheating the substrate prior to securing thesubstrate to the substrate support.
 4. The method of claim 3, whereinpreheating the substrate further comprises: preheating the substrate toa temperature within at least about 150 degrees Celsius of a targetedtemperature of the substrate at a pressure of about 8 Torr for aduration of at least about 50 seconds.
 5. The method of claim 2, furthercomprising: heating the substrate to provide a non-uniform temperatureprofile to the first layer; wherein the RF plasma has a non-uniformplasma profile and wherein the non-uniform temperature profile isselected to compensate for the non-uniform plasma profile.
 6. The methodof claim 1, wherein the process gas consists of ammonia (NH₃) and thenoble gas.
 7. The method of claim 6, wherein the process gas is about0.5-15 percent ammonia (NH₃) and about 85-99.5 percent argon.
 8. Themethod of claim 1, wherein the process gas consists essentially ofammonia (NH₃) and the noble gas.
 9. The method of claim 8, wherein theprocess gas is about 0.5-15 percent ammonia (NH₃) and about 85-99.5percent argon.
 10. The method of claim 1, wherein the process gas isabout 0.5 to about 10 percent ammonia (NH₃) and the balance isessentially the noble gas.
 11. The method of claim 1, wherein theprocess gas is about 1 to about 5 percent ammonia (NH₃) and the balanceis essentially the noble gas.
 12. The method of claim 1, wherein theprocess gas is about 2.5 percent ammonia (NH₃) and about 97.5 percentthe noble gas.
 13. The method of claim 1, wherein the first layerincludes silicon oxide (SiO₂), hafnium oxide (HfO₂), hafnium silicate(HfSiO_(x)), a first sub-layer of SiO₂ and a second sub-layer of HfO₂,or a first sub-layer of SiO₂ and a second sub-layer of HfSiO_(x). andwherein the nitrogen-containing layer comprises silicon oxynitride(SiON), hafnium oxynitride (HfON), or nitridized hafnium silicate(HfSiON).
 14. The method of claim 1, wherein heating the substratefurther comprises: heating the substrate utilizing a plurality ofresistive heating elements disposed in an electrostatic chuck that formspart of the substrate support, wherein the resistive heating elementsdefine multiple independently controllable heating zones; and heatingthe substrate in a desired pattern utilizing the independentlycontrollable heating zones to control a nitrogen dose pattern of thesubstrate.
 15. The method of claim 1, wherein the substrate is heated toa temperature of about 350 degrees Celsius to about 450 degrees Celsius.16. The method of claim 1, further comprising: exposing the first layerto a pre-conditioning plasma formed from a pre-conditioning gas, whereinthe pre-conditioning gas reduces residual oxygen content in the processchamber.
 17. The method of claim 16, wherein the pre-conditioning gasincludes an inert gas, hydrogen (H₂) and an inert gas, or ammonia (NH₃).18. The method of claim 1, wherein the substrate support comprises anelectrostatic chuck having a heater, and wherein heating the substratefurther comprises heating the substrate to a temperature of about 350 toabout 450 degrees Celsius using the heater while securing the substrateto the substrate support using the electrostatic chuck.
 19. A computerreadable medium, having instructions stored thereon that, when executed,causes a process chamber to perform a method of forming anitrogen-containing layer, the method comprising: exposing a first layerof a substrate to a plasma formed from a process gas comprisingpredominantly a mixture of ammonia (NH₃) and a noble gas, whereinammonia is about 0.5 to about 15 percent of the process gas and thenoble gas is predominantly the balance; and maintaining the processchamber at a pressure of about 10 mTorr to about 80 mTorr while exposingthe first layer to the plasma to transform at least an upper portion ofthe first layer into a nitrogen-containing layer.
 20. The computerreadable medium of claim 19, wherein the process gas consists of ammoniaand the noble gas.